Self administered subcutaneous or intramuscular injections are well known in the medical arts and have long been considered standard treatment for those persons, such as diabetics, who require fixed or measured doses of medicament on a regular and relatively frequent basis. Further, newer treatments, such as growth hormone injections, also require self administered injections on a regular basis.
Self administered injections considerably decrease the cost of treatment and increase the quality of the patients life by decreasing or even eliminating the need for some visits to the doctor. Self administered injections also provide patients with the opportunity to privately administer their own treatment, without involving third parties, thus giving the patient a sense of independence and control.
Typically, self administered injections were rendered using common syringes adapted to receive cartridges of pre-measured doses of medicament. However, such self administered injections suffered from several drawbacks and were particularly ill suited for use by children or patients with disabilities because they required the patient to manually insert an exposed needle in the tissue.
FIG. 1 is a cross-sectional view of a typical prior art injection pen 11. Injection pen 11 had three major components: (i) a pre-filled medicament cartridge assembly 10 containing a medicament 28; (ii) a cartridge housing 16 formed to receive pre-filled medicament cartridge assembly 10, and having a double sided needle assembly 13 mounted on one end 20; and (iii) a dispensing assembly 21. Each of the three major components are described more completely below. For a more complete description of a particular injection pen 11, see commonly assigned U.S. patent application Ser. No. 08/146,313 entitled "An Injection Pen Solution Transfer Apparatus and Method" of Peter Michel, Robert Freeman, James Oeswein filed on Nov. 2, 1993, which is incorporated herein by reference in its entirety.
End 12 of pre-filled medicament cartridge assembly 10 has a seal assembly 26 that is pierced and penetrated by needle 27 to dispense medicament 28. A second end 14 of pre-filled medicament cartridge assembly 10, that is opposite to end 12, is sealed by a slidable plunger 15.
Typically, cartridge housing 16 receives the pre-filled medicament cartridge assembly 10 through an open end 17. End 20 of cartridge housing 16, that is opposite open end 17, is generally removably mounted to double sided needle assembly 13 for subcutaneous or intramuscular injection of medicament 28. Removably mounted to end 17 is a dispensing assembly 21 that is operably coupled to cartridge plunger 15.
Specifically, a cartridge seat 22 of dispensing assembly 21 is formed to mount directly to sleeve 16, via mating threads 23. Upon mounting dispensing assembly 21 to cartridge housing 16, end 12 of medicament cartridge assembly 10 is forced into engagement with needle assembly 13. A pushrod 24, having a pushrod piston head 18, which abuts a backside 25 of plunger 15, is mounted to cartridge seat 22 to permit axial movement in a direction toward needle assembly 13. The movement of plunger 15 towards end 12 controls the volume of medicament expelled through needle assembly 13.
Prior art injection pen device 11 has no mechanism for allowing the introduction of an accurate dose less than the entire content of medicament cartridge assembly 10. Several improvements have been made on this basic design which deliver portions of medicament 28 in medicament cartridge assembly 10 in pre-set doses. However, the improved versions require considerable patient interaction with some form of relatively complicated dosing mechanism to set the dose with each injection.
Typically, prior art medicament injection devices require the patient to manually insert an exposed needle into his or her own tissue. For many patients this is a traumatic routine. Often injections are necessary on a daily basis which can result in considerable psychological damage to the patient and his or her attitude towards treatment. In many cases the patient simply stops giving himself or herself treatment; adopting the attitude that the cure is worse than the affliction. Patient non-compliance is a particularly poignant problem when the patient is a child and, unfortunately, children make up a considerable percentage of those patients taking part in treatment programs requiring self administered subcutaneous or intramuscular injections. For instance, at present, in the United States, growth hormone treatment is only approved for children. Additionally, many diabetics must begin insulin treatment at an early age.
Further, when a patient manually inserts a needle there is a strong possibility that the patient will not place the needle in the proper orientation relative to the skin. The needle typically should enter the body perpendicular to the skin surface. If the patient is traumatized by the treatment routine, or is under time pressure, a sloppy and ineffective injection is likely to result from a non-perpendicular injection. When the needle enters the tissue at the wrong needle/skin orientation the injection may fail to properly introduce the medicament. Such improperly oriented injections, of course, are, at best, a waste of costly medicament and, at worst, may be dangerous.
Yet another difficulty with prior art injection pens is that the dose-setting mechanisms are complicated and usually involve reading some form of digital or analog meter while setting the dose. These prior art injection pens do not allow the patient to accurately set the dose in the event that the patient is either disabled or in a state incapable of reading a dose meter or setting some relatively complicated analog device.
Prior art dose-setting mechanisms using dose meter displays alone are a particular problem for diabetics who, because of their disease, are often blind. However, any patient who is either permanently or temporarily disabled, or is in an emergency situation, may find prior art dose mechanisms inadequate or perhaps useless.
Another problem is that two different unit systems for measuring the dose are commonly used; milliliters (ml) and international units (IU). In some cases, the patient can become confused as to which units the prior art dose meter is displaying. This situation can lead to improper dosage which, of course, is dangerous. Thus, while prior art injection pens are better than a syringe, such injection pens are not suitable for use in a wide variety of circumstances.